Method and system for multi-user transmit opportunity for multi-user multiple-input-multiple-output wireless networks

ABSTRACT

Wireless communication in a wireless system using a multiple user transmission opportunity is provided. Data blocks at a wireless station are transmitted to multiple wireless receivers over a shared wireless communication medium. The data blocks are organized in order of transmission priority based on access categories. Contention for access to the communication medium during a transmission opportunity period is based on a backoff timer of each access category and the transmission priority. Upon successful contention for a transmission opportunity period, during the transmission opportunity period, a data block of a primary access category is wirelessly transmitted from the wireless station to one or more primary destination wireless receivers. Simultaneously, a data block of a secondary access category is wirelessly transmitted from the wireless station to one or more secondary destination wireless receivers.

RELATED APPLICATION

This application claims priority from U.S. Provisional PatentApplication Ser. No. 61/325,762 filed Apr. 19, 2010, and from U.S.Provisional Patent Application No. 61/362,280 filed Jul. 7, 2010, bothincorporated herein by reference.

FIELD

The present disclosure relates generally to the field of wirelessnetworks, and in particular, to wireless networks where multipleantennas are used to transmit multiple downlink traffic streams tomultiple receiver stations simultaneously.

BACKGROUND

In a typical wireless network utilizing a coordination function forcoordinating transmissions among wireless stations, such a coordinationfunction may be implemented in one of the wireless stations such as awireless access point (AP) functioning as a coordinator. The wirelessstations may communicate via directional transmissions using sectorantennas and beam-forming antenna arrays. The coordinator may useomnidirectional transmissions for broadcasts to all wireless stations inall directions (e.g., 360 degrees range).

Alternatively, the coordinator may use quasi-omnidirectionaltransmissions for broadcasts to a wide range, but not necessarily in alldirections. In many wireless area networks (WLANs) such as thoseaccording to IEEE 802.11 standards, a coordinator is used ininfrastructure mode for providing contention-free access to a wirelesscommunication medium to support Quality of Service (QoS) for certainapplications.

BRIEF SUMMARY

Embodiments provide wireless communication in a wireless network using amultiple user transmission opportunity. One embodiment comprisesmaintaining data blocks at a wireless transmitting station fortransmission to multiple wireless receiving stations over a sharedwireless communication medium, wherein the data blocks are organizedbased on access categories.

Access to the communication medium includes contending for access to thewireless communication medium. Upon successful contention for atransmission opportunity period, during the transmission opportunityperiod, one or more data blocks of a primary access category aretransmitted from the transmitting station to one or more primarydestination wireless receiving stations, through one or more sets ofspatial streams, over the wireless communication medium.

In one embodiment, one or more data blocks of one or more secondaryaccess categories are simultaneously transmitted from the transmittingstation to one or more secondary destination wireless receivingstations, via one or more sets of spatial streams over the wirelesscommunication medium. Multiple frame transmissions take place if thetransmission opportunity limit of the primary access category has notbeen reached.

These and other features, aspects and advantages will become understoodwith reference to the following description, appended claims andaccompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary block diagram of a wireless systemimplementing multi-user transmit opportunity (MU-TXOP) for multi-usermultiple-input-multiple-output (MU-MIMO) communication.

FIG. 2A shows an example access category (AC) scenario at an accesspoint (AP) station for simultaneous frame transmission to multipledestination stations during a MU-TXOP over a wireless communicationmedium.

FIG. 2B shows an example timing diagram of frame exchange sequencecorresponding to FIG. 2A.

FIG. 3A shows an exemplary diagram of a wireless system implementingMU-TXOP for MU-MIMO communication, according to an embodiment of thepresent invention.

FIG. 3B shows an exemplary timing diagram of wireless channel access andtransmission sequence in a MU-TXOP for MU-MIMO communication.

FIG. 4 shows an exemplary flowchart of a frame exchange process usingMU-TXOP in a wireless system implementing MU-MIMO.

FIG. 5 shows an exemplary timing diagram of wireless channel access andtransmission sequence in a MU-TXOP for MU-MIMO communication accordingto the process in FIG. 4.

FIG. 6 is an exemplary high level block diagram showing an informationprocessing system comprising a computer system useful for implementingdisclosed embodiments.

DETAILED DESCRIPTION

Embodiments provide a method and system for simultaneously transmittingmultiple downlink spatial streams to multiple receiver wireless stationsduring a multi-user transmit opportunity over a wireless communicationmedium.

Generally in the absence of a coordinator, contention-free access to awireless communication (e.g., a radio frequency (RF) channel) may beimplemented using announcement or information exchange among wirelessstations in a network to negotiate/reserve the use of the communicationmedium. For example, IEEE 802.11e Enhanced Distributed Channel Access(EDCA) provides QoS support for certain applications using announcementor information exchange. EDCA defines four Access Categories (ACs) andintroduces service differentiation such that certain data traffic useshigher priority parameters to contend for the communication medium.

Further, a frame structure may be used for data transmission betweenwireless stations such as a transmitter station and a receiver station.In one example, a frame structure in a Media Access Control (MAC) layerand a physical (PHY) layer is utilized, wherein in a transmitterstation, a MAC layer receives a MAC Service Data Unit (MSDU) andattaches a MAC header thereto, in order to construct a MAC Protocol DataUnit (MPDU). The MAC header includes information such as a sourceaddress (SA) and a destination address (DA). The MPDU is a part of a PHYService Data Unit (PSDU) and is transferred to a PHY layer in thetransmitter to attach a PHY header (i.e., PHY preamble) thereto toconstruct a PHY Protocol Data Unit (PPDU). The PHY header includesparameters for determining a transmission scheme including acoding/modulation scheme. The PHY layer includes transmission hardwarefor transmitting data bits over a wireless link. Before transmission asa frame from the transmitter station to the receiver station, a preambleis attached to the PPDU, wherein the preamble can include channelestimation and synchronization information.

EDCA allows contention for transmission opportunities (TX0Ps), wherein aTXOP is a time interval when a quality of service (QoS) wireless station(STA) may initiate frame transfer on the wireless medium (e.g., wirelesschannel). The TXOP may be assigned to the wireless station by acoordinator, or the wireless station may obtain the TXOP by successfullycontending for the wireless channel.

Conventionally, a single user TXOP (SU-TXOP) defined in IEEE 802.11standards is utilized per AC. As such, a SU-TXOP obtained by a stationonly sets the Network Allocation Vector (NAV) timer for a specific AC(used to contend for the TXOP), to idle during the SU-TXOP period. NAVsfor other Access Categories of the same station are set to busy. NAV isa counter maintained by each station, indicating the time to elapseuntil the channel is free again, such that a station cannot transmituntil its NAV is zero. An EDCA TXOP is granted to Enhanced DistributedChannel Access Function (EDCAF) when the EDCAF determines that it mayinitiate a frame exchange sequence. During an EDCA SU-TXOP, a wirelessstation may initiate multiple frame exchange sequences to transmit MACManagement Protocol Data Units (MMPDUs) and/or MSDUs only within thesame AC.

Internal contention among frames belonging to different ACs allows onlyone AC to win the internal competition for the TXOP

Disclosed embodiments provide a multi-user transmit opportunity(MU-TXOP) mechanism for a wireless communication system such as wirelessnetwork to support multiple downlink traffic streams to multiplereceiver wireless stations simultaneously during the MU-TXOP (i.e., ashared transmission opportunity period). According to an embodiment,contention among access categories is resolved, in some cases, byallowing access categories to share a transmission opportunity period.

According to an embodiment, data blocks are maintained at a wirelesstransmitting station for transmission to multiple wireless receivingstations over a wireless medium. The data blocks are organized accordingto their access category, which assigns different transmissionpriorities to the data blocks. EDCAF of each AC of the transmittingstation contends for access to the wireless medium based on its backofftimer value and transmission priority.

In one embodiment, an access category is divided into two classes when aTXOP is shared: a primary AC and a secondary AC. The destinationwireless stations are divided into two classes, the primary destinationand the secondary destination. When contending for transmissionopportunity, only the EDCA parameters of the primary AC are used, notthe combination of all ACs that have buffered data, or the EDCAparameters of the highest priority AC.

Upon successful contention for a transmission opportunity period, duringthe transmission opportunity period, one or more data blocks of aprimary access category are transmitted from the transmitting station toone or more primary destination wireless receiving stations through oneor more sets of spatial streams over the wireless communication medium.Simultaneously, one or more data blocks of one or more secondary accesscategories are transmitted from the transmitting station to one or moresecondary destination wireless receiving stations, through one or moreother sets of spatial streams over the wireless communication medium.Multiple frame transmissions are possible provided that the TXOP limitof the primary AC has not been reached.

In the description herein primary AC comprises an AC that wins the TXOPfor channel access after both external and internal competition. Therecan be only one primary AC at any moment. Secondary AC comprises an ACwhich does not win a TXOP but wishes to share the TXOP obtained by theprimary AC for simultaneous transmissions. There can be multiplesecondary ACs at any moment. Primary destinations comprise destinationstargeted by frames belonging to the primary AC. There can be one or moreprimary destinations at any moment. Secondary destinations comprisedestinations targeted by the frames belonging to secondary ACs. Therecan be one or more secondary destinations at any moment.

According to an embodiment, internal contention among access categoriesis resolved by allowing secondary ACs to share A TXOP. When sharing aTXOP is not possible, the secondary AC invokes backoff.

Disclosed embodiments provide a method of wireless communication in awireless communication system, comprising: receiving data blockstransmitted from a transmitting station over a wireless communicationmedium, wherein the data blocks are organized based on primary andsecondary access categories; extracting, from the received data blocks,data blocks of the primary access category; and processing the datablocks of the primary access category.

According to an embodiment, the data blocks are organized into theprimary and secondary access categories in order of transmissionpriority; and the transmitting station comprises amultiple-input-multiple-output (MIMO) wireless station.

According to an embodiment, each data block comprises a packet includingan address of a receiving station, and the method further comprisestransmitting an acknowledgement after receiving a corresponding packetof the receiving station.

Disclosed embodiments provide a method of wireless communication in awireless communication system, comprising: receiving data blockstransmitted from a transmitting station over a wireless communicationmedium, wherein the data blocks are organized based on primary andsecondary access categories; extracting, from the received data blocks,data blocks of the secondary access category; and processing the datablocks of the secondary access category.

Disclosed embodiments provide a method of wireless communication in awireless communication system, comprising: receiving data blockstransmitted from a transmitting station over a wireless communicationmedium, wherein the data blocks are organized based on the primary andsecondary access categories; extracting, from the received data blocks,data blocks of the primary access category and data blocks of thesecondary access category; and processing the extracted data blocks ofthe primary access category and the secondary access category.

FIG. 1 shows an exemplary wireless network 10. The wireless networkcomprises a wireless local area network (WLAN) comprising multiplewireless stations. A wireless station 11 (i.e., STA-A) comprises anaccess point (AP) having a PHY layer 14 and a MAC layer 12 implementingan EDCA MU-TXOP module (i.e., channel access module) 16. Several trafficstreams (or queues) of data frames (packets) in multiple differentaccess categories ACs at the AP station 11 are for transmission tomultiple receiver wireless stations 13. Each wireless station 13comprises a MAC layer 13M and a PHY layer 13P.

In this example, there are three traffic streams (or queues) of dataframes (packets) in three different access categories AC0, AC1, and AC2at the AP station 11 for transmission to receiver wireless stations 13(i.e., STA-B, STA-G and STA-D), respectively. AC0 is a primary AC, andAC1 and AC2 are secondary ACs.

MU-TXOP according to the invention is useful in both EDCA and hybridcoordination function controlled channel access (HCCA). The exampleembodiments described herein are for EDCA, wherein a MU-TXOP is assignedto a multi-user multiple-input-multiple-output (MU-MIMO) wirelessstation such as the AP station 11 in FIG. 1.

In one embodiment, the EDCA MU-TXOP module 16 implements three modes. Afirst mode involves initiation of the EDCA MU-TXOP which occurs when theEDCA rules permit access to the wireless communication medium (e.g.,wireless radio frequency (RF) channel). A second mode involves sharingof the EDCA MU-TXOP which occurs after an Enhanced Distributed ChannelAccess Function (EDCAF) is granted the TXOP. A third mode involvesmultiple frame transmission within an EDCA MU-TXOP, which occurs when anEDCAF retains the right to access the wireless communication mediumfollowing the completion of a frame exchange sequence, such as onreceipt of multiple block acknowledge (BA) frames from receivingwireless stations 13. The three examples EDCA MU-TXOP modes aredescribed further below.

In one embodiment, an initiation of the MU-TXOP occurs when the EDCArules permit access to the wireless communication medium. Although theremay be other factors that affect the transmission decision (such asscheduling), in general, the EDCAF of an AC of the transmitting APstation 11 is allowed to access the wireless communication medium if allthe following conditions are satisfied:

-   -   1) The backoff timer of the AC has counted down to zero when the        backoff slot boundary is reached;

2) The AC has higher priority than other ACs;

3) The AC has buffered data to transmit.

When an AC is allowed to access the wireless communication medium afterwinning both the external (with other STAB) and the internal (with otherACs of the same STA) competition, it becomes the primary AC. An EDCAMU-TXOP is granted to the EDCAF of this AC. Other ACs become secondaryACs and may be able to share the obtained EDCA MU-TXOP.

According to an embodiment, when contending with other stations fortransmission opportunity for access to the wireless communication medium(e.g., radio frequency wireless channel), the rules the AP station 11uses remain the same as in the conventional IEEE 802.11 wirelesscommunication specifications. Each AC of the AP station uses a set ofEDCA parameters of this AC (e.g., AIFS[AC]) to contend for wirelesschannel access.

The AP station 11 may not always use its highest priority AC forcontending the TXOP even though the highest priority AC may be able toshare the TXOP for simultaneous transmission. Otherwise, such a behaviorby AP station 11 in using its highest priority AC for contending theTXOP, will break the fairness of EDCA access rules and other non-APstations (such as stations 13) will have less chance and less time fortransmission.

In one embodiment, the ACs (e.g., AC0, AC1, AC2) at the AP station 11are divided into two classes: primary AC and secondary AC. A primary ACis an AC that wins both external competition among multiple wirelessstations (STAB) 13, and internal competition among multiple ACs at theAP station 11. The primary AC is not always the highest priority AC(e.g., AC0 in FIG. 1) even though the highest priority AC has a betterchance to become a primary AC. The primary AC is the “actual holder” ofthe MU-TXOP. Secondary ACs include the remaining ACs at the AP station(e.g., AC1, AC2). The frames of the secondary ACs share the MU-TXOP withthe frames of the primary AC, for essentially simultaneous transmissionfrom the AP station 11 to multiple receiver stations 13 over thewireless channel.

The destination wireless stations 13 targeted by the frames of theprimary AC at the AP station 11 are defined as primary wireless stationdestinations. If the frames of the primary AC target more than onedestination wireless station, there will be multiple primarydestinations. The destination wireless stations 13 only targeted byframes of secondary ACs are defined as secondary destinations. When theframes of the primary AC and frames of one or more secondary ACs targetthe same destination wireless station, the destination wireless stationis still a primary destination and the frames of the secondary ACs mustyield to the frames of the primary AC.

According to an embodiment, sharing of a MU-TXOP allows secondary ACs totransmit their data frames in the TXOP period obtained by the primary ACat the AP station 11. In one embodiment, sharing takes place when thefollowing conditions are satisfied:

1) Frames for multiple STAs exist.

2) Downlink multiuser MIMO (DL MU-MIMO) transmission is possible:

If, for example, the primary AC and one or more ACs have framestargeting to the same destination STA, then DL MU-MIMO transmission isnot possible. In this case, single user MIMO (SU-MIMO as in conventionalIEEE 802.11 n standard) can be used for transmitting the data of theprimary AC at the AP station 11 and a secondary AC cannot share theTXOP.

3) DL MU-MIMO transmission is appropriate:

In certain cases, both conditions 1) and 2) above are met, but it isstill not appropriate to use MU-MIMO protocol and share MU-TXOP. Forexample, when two or more destination STAs 13 targeted by both primaryand secondary AC at the AP station are spatially too close to each other(exposing the stations to potential RF interference), then SU-MIMO is amore appropriate transmission protocol at the AP station 11.

In one embodiment, sharing a MU-TXOP is performed by grouping of thewireless stations 13, wherein the primary wireless station destinationsare grouped with one or more secondary wireless station destinations.The MAC layer 12 at the AP station 11 can group one or more primarywireless station destinations with one or more secondary wirelessstation destinations in different ways. In one implementation, a GrouplDcan be assigned to a selected group of wireless station destinations andutilized to identify them. Each wireless station in the selected grouphas knowledge of the group definition (i.e., GroupID) prior to datatransmission for correct reception of the data frames at such wirelessstation destinations 13.

Once secondary wireless station destinations are selected, thecorresponding secondary ACs at the AP station 11 treat the wirelesschannel as idle to allow simultaneous transmissions.

Internal competition among the ACs at the AP station 11 for a TXOP isresolved by allowing secondary ACs to transmit in the same TXOP of theprimary AC. However, in certain cases simultaneous transmissions are notpossible. In one of such cases, frames of different ACs transmitting tothe same destination wireless stations. In another such case, thetransmission time of the secondary ACs is longer than that of theprimary AC at the AP station 11, wherein the secondary AC is unwillingto fragment the frame (or it is not possible to fragment). In that case,the additional time taken by the secondary AC for transmission may leadto unfairness to other stations in the WLAN Basic Service Set (BSS).

When parallel (i.e., simultaneous) transmission is not possible at theAP station 11, a lower priority AC backs off as in the conventional IEEE802.11 standard. The primary AC may choose to use SU-MIMO for its owntransmission, after the lower priority AC backs off. In one embodiment,a scheduler 18 at the AP station (FIG. 1) determines which frames (datablocks) 15 are to be transmitted to multiple receiver stations, whereinthe frames are organized into ACs based on QoS rules, and arranged intoqueues accordingly. A manager module 19 determines the primary AC to beused for contending for a transmission opportunity.

FIGS. 2A-2B show an example wherein data frames in different ACs at theAP station 11 (FIG. 2A) can share the MU-TXOP,. In FIG. 2A, it isassumed that AC_VI is the primary AC having two sets of MSDU frames 15(e.g., AC_VI(1) and AC_VI(2)) in memory buffer to wirelessly transmit,one for destination station STA-B and the other for destination stationSTA-D. As such, both destination STA-B and STA-D are primarydestinations. AC_VO and AC_BE are secondary ACs, and destination STA-Cis a secondary destination.

Further, AC_VO has two sets of MSDU frames for transmission, a first setAC_VO(1) for transmission to destination STA-D and a second set AC_VO(2)for transmission to destination STA-C. In addition, AC_BE has two setsof MSDU frames, a first set AC_BE(1) for transmission to destinationSTA-C and a second set AC_BE(2) for transmission to destination STA-D. Aremaining AC_BK has no frames to transmit. FIG. 2B shows a correspondingtransmission process 20 for the aforementioned MSDU frames from theprimary and secondary ACs in AP station 11 using a shared MU-TXOP over awireless communication channel to the destination wireless stations 13in a frame exchange sequence. The wireless stations 13 may transmitresponsive frames (e.g., acknowledgment (ACK) frames) back to the APstation 11 over the wireless communication medium.

The MSDU frames 15 in memory buffer at the AP station 11 may befragmented or aggregated into multiple A-MPDUs, each being transmittedin one downlink phase.

According to an embodiment, once a MU-TXOP is granted to the AP station11, in a frame exchange sequence with destination stations 13, theframes associated with different ACs at the AP station 11 share thatMU-TXOP for downlink transmissions to multiple wireless stations 13,wherein all the transmissions take place at the same time via differentspatial streams over the wireless communication medium. Therefore, theMU-TXOP is shared among multiple set of spatial streams (each settargeting one destination station) that can belong to multiple ACs forthe downlink transmission from the AP station 11 to multiple destinationwireless stations 13. Unlike SU-TXOP, data frames belonging to secondaryACs that are scheduled to be transmitted with that of the primary AC usethe same TXOP for transmission at the AP station 11.

In one example in the network 10 of FIG. 1, during a MU-TXOP, multipletraffic/transmission streams/paths belonging to different accesscategories ACO, AC1, AC2 at the AP station 11 are transmittedsimultaneously over a wireless communication medium to multiple wirelessstations 13 (i.e., STA-B, STA-C and STA-D) over multiple wirelessstreams/paths (i.e., Path1, Path2, Path3). The AP station 11 implementsmulti-user multiple-input-multiple-output (MIMO) at its PHY layer 14 forsuch simultaneous wireless transmissions via multiple antennas 17 to thewireless stations 13 over the wireless communication medium.

In one embodiment, the MU-TXOP module 16 at the MAC layer of the APstation 11 comprise protocols, hardware and/or software implementations,which support downlink (DL) multi-user MIMO (DL MU-MIMO) wirelesscommunication to the wireless stations 13 over the wirelesscommunication medium. In the network 10, DL MU-MIMO wirelesscommunication allows a sender station such as the AP station 11 toobtain a MU-TXOP for simultaneously transmitting frames 15 in AC0, AC1and AC2 via multiple traffic streams to different receiving wirelessstations 13 such as STA-B, STA-C, STA-D, using directional transmissionvia the wireless communication medium. In one embodiment, multi-userdirectional transmissions using beam-forming are utilized between the APstation 11 and each of the multiple wireless stations 13 (i.e., STA-B,STA-C, STA-D). Beam-steered wireless signals comprise directional beamsignals, wherein each directional beam (i.e., path) comprises a mainlobe and side lobes.

In one embodiment, the TXOP duration is determined by the TXOP limit ofthe primary AC. At least one spatial stream set in each DL MU-MIMO PPDUcontains only MSDU(s) corresponding to the primary AC, wherein a streamset is defined as a group of spatial streams of a DL MU-MIMO PPDU thatare all intended for reception by a single recipient station. As usedherein, PPDU stands for physical (PHY) layer convergence procedure(PLCP) protocol data unit.

FIG. 3A illustrates an example downlink transmission in the wirelessnetwork 10 involving multi-user MIMO transmission of frames B, C, D fromthe AP station 11 (STA-A) to the receiver stations STA-B, STA-C, STA-Dduring a MU-TXOP, respectively, via directional transmissions over thewireless communication medium.

FIG. 3B shows a timing diagram 25 for the example communication in FIG.3A, wherein during a MU-TXOP in a downlink phase, the AP station 11(STA-A) simultaneously directionally transmits three frames B, C, D(each with a specified destination receiver station address (RA)) to thereceiver stations 13 (STA-B, STA-C and STA-D), respectively. In anuplink phase, each of the receiver stations 13 sends a blockacknowledgement (BA) to the AP station 11 sequentially using apredefined schedule, over the wireless communication medium.

During an EDCA MU-TXOP obtained by an EDCAF at the AP station 11, theMU-MIMO AP station 11 may initiate multiple frame exchange sequenceswith destination wireless stations 13 to transmit MMPDUs and/or MSDUsbelonging to different ACs. For each frame exchange sequence, there canbe multiple simultaneous spatial streams targeting different receiverstations 13, belonging to different ACs at the AP station 11.

The MU-TXOP process according to an embodiment, allows frames belongingto different ACs at the AP station 11 to be transmitted using a TXOPobtained for the frames of the primary AC at the AP station 11. In oneimplementation, frames 15 belonging to a lower priority AC at the APstation 11 can share the TXOP as long as such frames are essentially ofsimilar length as that of the primary AC. As such throughput can beincreased without negatively affecting application quality of service(QoS) rules for the involved frames 15. Using frames of similar lengthprovides an AP the flexibility to select among the secondary AC framesfor transmission.

A MU-TXOP is obtained only using EDCA parameters of the primary AC atthe AP station 11, neither a combination of all ACs involved, nor alwaysthe highest priority AC that has frames to transmit. Though a MU-TXOP isobtained using EDCA parameters of the primary AC, the MU-TXOP is sharedby multiple traffic streams from the AP station 11 to the destinationstation 13, which may or may not belong to that AC.

In one embodiment, the same GrouplD for the selected destinationstations 13 is used to identify the destination stations 13 during theentire multiple frame exchange sequence between the AP station 11 andthe destination stations 13. In an alternative embodiment, GrouplD maybe changed during the multiple frame exchange sequence. This may be moreefficient when the number of destination stations 13 is large (e.g.,larger than 4) and the TXOP duration is long.

In one embodiment, multiple frame exchanges may be performed between theAP station 11 and the destination stations 13 when the primary ACpossesses remaining frames to transmit in its buffer (queue). In oneembodiment, once the primary AC at the AP station completes itstransmission, the MU-TXOP terminates even if secondary ACs possesremaining frames 15 in their buffers. As such, secondary ACs cantransmit their frames as long as the primary AC has not completedtransmission of its frames at the AP station 11. Once the primary AC hascompleted transmission of its frames, the frames of secondary ACs cannotbe transmitted and need to await a next MU-TXOP. When the primary ACcompletes its frame transmission, the MU-TXOP can be terminated by theMU-MIMO AP station 11 by transmitting a contention-free end (CF-End)frame over the wireless communication medium if the remaining time issufficient for transmission of such a CF-End frame.

In one embodiment of the invention, to transmit frames 15 of differentACs from the AP station 11 to different destination station 13, theframes may be aggregated into one Aggregated MAC Protocol Data Unit(A-MPDU) utilizing a frame aggregation process, and utilizing amulti-traffic block ACK (MTBA). In one implementation, as illustrated bythe timing diagram 50 in FIG. 5, short interframe spaces (SIFSs) may beused to separate frames between downlink transmission (from AP station11 to a destination station 13) and uplink transmission (from adestination station 13 to AP station 11) phases, as well as multipleresponse frames (i.e., clear-to-send or CTS) on responsive uplinktransmissions. The assumptions for FIG. 5 are the same as that for FIGS.2A-2B. In FIG. 5, a scheduled Block Acknowledgement (BA) scheme is usedfor the uplink phase, which does not prevent other acknowledgementsschemes to be utilized (e.g., a poll-based acknowledgement scheme).

In one embodiment, frame fragmentation or aggregation may be applied toframes for secondary ACs at the AP station 11 such that the transmissiontime of frames for secondary ACs are similar to that of the frames ofthe primary AC for each frame exchange sequence. In one embodiment ofthe invention, all stations 11 and 13 contend for transmissionopportunity again after a MU-TXOP ends.

In one embodiment, the duration of EDCA MU-TXOP is bounded by theprimary AC at the AP station 11. Such duration can be as defined by IEEE802.11 standards based on dot11QAPEDCATXOPLimit MIB variable for anaccess point. A value of 0 for EDCA MU-TXOP duration means that the EDCAMU-TXOP is limited to a single frame exchange sequence, in time domain,at any transmission rate in the operational set of the BSS. The APstation 11 may transmit multiple frames in the spatial domain tomultiple receiver stations 13, wherein each frame is carried by aspatial stream set. Each spatial stream set contains a group of spatialstreams of a downlink MU-MIMO PPDU that are all intended for receptionby a single receiver station 13. In one embodiment, at least one streamset in each DL MU-MIMO PPDU contains only MSDU(s) corresponding to theprimary AC. This is to ensure that the AP does not transmit only framesof secondary ACs during any downlink phase.

FIG. 4 shows an exemplary flowchart of a process 30 for frame exchangebetween an AP station (such as AP station 11) and destination wirelessstations (such as stations 13) using MU-TXOP. The example timing diagramin FIG. 5 may be based on the frame sequence exchange process 30according in FIG. 4, wherein frames to destination STA-B have thehighest AC priority (primary AC). Referring to process 30 in FIG. 4, inconjunction with FIG. 5, in block 31A, a collision protection mechanismsuch as request-to-send (RTS) and CTS protocol is utilized to preventpacket collision on a shared wireless communication channel. In block31B, group definition information through management frame (if anyneeded) is provided. In block 31C, channel sounding (if any needed) isperformed.

In block 32, during an assigned MU-TXOP, the AP station 11 performsdownlink transmission of a first frame sequence for all ACs at the APstation 11 to multiple receiver stations 13 via multiple spatialstreams. In block 33, the AP station 11 receives acknowledgmentresponses (e.g., BA) from the receiver stations 13. In block 34, the APstation 11 determines if the primary AC frames have completedtransmission. If not, in block 35 it is determined if there issufficient time remaining in the MU-TXOP for remaining frames at the APstation 11. If sufficient time remains in the MU-TXOP, then in block 36,a next frame sequence of the primary AC and any remaining secondary ACs,are transmitted from the AP station 11 to receiver stations 13 viamultiple spatial streams, and the process proceeds to block 33.

If insufficient time remains in the MU-TXOP for AC frame transmission,then the process proceeds to block 37 wherein it is determined if theremaining time is sufficient for transmission of a CF-End frame. If yes,then in block 38 the MU-TXOP is terminated (truncated) by transmissionof a CF-End frame from the AP station 11 to all destination stations 13.Further, if in block 34 it is determined that the primary AC frames haveall been transmitted, then the process proceeds to block 37. In theexample shown in FIG. 5, after AC frame transmissions, at the end of theMU-TXOP, the remaining time is insufficient for transmitting a CF-Endframe. Note that frames belonging to secondary ACs may be longer orshorter than frames of the primary AC at each frame exchange sequence.Further, the terms “stream” and “path” need not be equivalent. Forexample, it is possible that an AP uses multiple streams to transmit toone STA.

As is known to those skilled in the art, the aforementioned examplearchitectures described above, can be implemented in many ways, such asprogram instructions for execution by a processor, as software modules,microcode, as computer program product on computer readable media, aslogic circuits, as application specific integrated circuits, asfirmware, as consumer electronic devices, etc., in wireless devices, inwireless transmitters/receivers, in wireless networks, etc. Further,embodiments can take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing both hardwareand software elements.

FIG. 6 is a high level block diagram showing an information processingsystem comprising a computer system 100 useful for implementingdisclosed embodiments. The computer system 100 includes one or moreprocessors 101, and can further include an electronic display device 102(for displaying graphics, text, and other data), a main memory 103(e.g., random access memory (RAM)), storage device 104 (e.g., hard diskdrive), removable storage device 105 (e.g., removable storage drive,removable memory module, a magnetic tape drive, optical disk drive,computer readable medium having stored therein computer software and/ordata), user interface device 106 (e.g., keyboard, touch screen, keypad,pointing device), and a communication interface 107 (e.g., modem, anetwork interface (such as an Ethernet card), a communications port, ora PCMCIA slot and card). The communication interface 107 allows softwareand data to be transferred between the computer system and externaldevices. The system 100 further includes a communications infrastructure108 (e.g., a communications bus, cross-over bar, or network) to whichthe aforementioned devices/modules 101 through 107 are connected.

Information transferred via communications interface 107 may be in theform of signals such as electronic, electromagnetic, optical, or othersignals capable of being received by communications interface 107, via acommunication link that carries signals and may be implemented usingwire or cable, fiber optics, a phone line, a cellular phone link, anradio frequency (RF) link, and/or other communication channels. Computerprogram instructions representing the block diagram and/or flowchartsherein may be loaded onto a computer, programmable data processingapparatus, or processing devices to cause a series of operationsperformed thereon to produce a computer implemented process.

Embodiments have been described with reference to flowchartillustrations and/or block diagrams of methods, apparatus (systems) andcomputer program products. Each block of such illustrations/diagrams, orcombinations thereof, can be implemented by computer programinstructions. The computer program instructions when provided to aprocessor produce a machine, such that the instructions, which executevia the processor create means for implementing the functions/operationsspecified in the flowchart and/or block diagram. Each block in theflowchart/block diagrams may represent a hardware and/or software moduleor logic. In alternative implementations, the functions noted in theblocks may occur out of the order noted in the figures, concurrently,etc.

The terms “computer program medium,” “computer usable medium,” “computerreadable medium”, and “computer program product,” are used to generallyrefer to media such as main memory, secondary memory, removable storagedrive, a hard disk installed in hard disk drive, and signals. Thesecomputer program products are means for providing software to thecomputer system. The computer readable medium allows the computer systemto read data, instructions, messages or message packets, and othercomputer readable information from the computer readable medium. Thecomputer readable medium, for example, may include non-volatile memory,such as a floppy disk, ROM, flash memory, disk drive memory, a CD-ROM,and other permanent storage. It is useful, for example, for transportinginformation, such as data and computer instructions, between computersystems. Computer program instructions may be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

Furthermore, the computer readable medium may comprise computer readableinformation in a transitory state medium such as a network link and/or anetwork interface, including a wired network or a wireless network, thatallow a computer to read such computer readable information. Computerprograms (i.e., computer control logic) are stored in main memory and/orsecondary memory. Computer programs may also be received via acommunications interface. Such computer programs, when executed, enablethe computer system to perform the features as discussed herein. Inparticular, the computer programs, when executed, enable the processormulti-core processor to perform the features of the computer system.Such computer programs represent controllers of the computer system.

Though the embodiments have been described with reference to certainversions thereof; however, other versions are possible. Therefore, thespirit and scope of the appended claims should not be limited to thedescription of the preferred versions contained herein.

1. A method of wireless communication in a wireless communication system, comprising: maintaining data blocks at a wireless transmitting station for transmission to multiple wireless receiving stations over a wireless communication medium, wherein the data blocks are organized based on access categories; each access category contending for a transmission opportunity period for access to the wireless communication medium; and upon successful contention, during the transmission opportunity period transmitting one or more data blocks of a primary access category from the transmitting station to one or more primary destination wireless receiving stations, simultaneously transmitting one or more data blocks of one or more secondary access categories from the transmitting station to one or more secondary destination wireless receiving stations, over the wireless communication medium.
 2. The method of claim 1, wherein: the data blocks are organized into access categories in order of transmission priority; and the transmitting station comprises a multiple-input-multiple-output (MIMO) wireless station.
 3. The method of claim 2, wherein the transmission opportunity comprises a multi-user transmission opportunity (MU-TXOP) for simultaneous transmission of data blocks at different transmission priorities during the MU-TXOP, over the wireless communication medium.
 4. The method of claim 1, wherein: contending for the transmission opportunity period comprises each access category contending for access to the wireless communication medium based on a value of a respective backoff timer and transmission priority; and transmitting during the transmission opportunity period comprises directionally transmitting the data blocks of the primary access category from the transmitting station to the one or more primary destination receiving stations over the wireless communication medium while simultaneously transmitting the data blocks of the one or more secondary access categories from the transmitting station to the one or more secondary destination receiving stations over the wireless communication medium.
 5. The method of claim 3, wherein: contending for access to the wireless communication medium comprises performing Enhanced Distributed Channel Access (EDCA) to provide Quality of Service (QoS) for a data block in a high priority access category.
 6. The method of claim 1, wherein: contending for a transmission opportunity period comprises performing Enhanced Distributed Channel Access (EDCA) to provide Quality of Service (QoS) for a data block in the primary access category; and transmitting during the transmission opportunity period comprises directionally transmitting the data blocks of the primary access category from the transmitting station to the one or more primary destination wireless receiving stations over the wireless communication medium, and simultaneously, transmitting the data blocks of the secondary access categories from the transmitting station to the one or more secondary destination wireless receiving stations over the wireless communication medium.
 7. The method of claim 1, wherein: each data block comprises a packet including an address of a destination wireless receiving station; and the method further comprising receiving an acknowledgment from each destination wireless receiving station after transmitting a packet intended for each destination wireless receiving station.
 8. The method of claim 7, further comprising: truncating the transmission opportunity upon transmission of a last data block of the primary access category.
 9. The method of claim 8, wherein: the transmitting station performs multi-user MIMO wireless transmission via multiple antennas over the wireless communication medium.
 10. The method of claim 9 wherein the wireless communication system comprises a wireless local area network.
 11. The method of claim 6, wherein: a duration of the transmission opportunity period is based on a transmission opportunity period limit of the primary access category; at least one spatial stream set in each downlink multi-user MIMO physical layer convergence procedure (PLOP) protocol data unit (PPDU) packet includes only one or more MAC service data unit (MSDU) packets corresponding to the primary access category, wherein a stream set comprises a group of spatial streams of a downlink MU-MIMO PPDU packet intended for reception by a single destination receiving wireless station over the wireless communication medium.
 12. The method of claim 6, wherein: in contending for the transmission opportunity period only EDCA parameters of the primary access category are used.
 13. The method of claim 1, further comprising: resolving internal contention among the access categories by allowing secondary access categories to share the transmission opportunity period.
 14. The method of claim 13, wherein when sharing a transmission opportunity period is not possible, the secondary access categories invoking communication medium access backoff.
 15. A wireless station for wireless communication in a wireless communication system, comprising: a communication physical layer configured for wireless communication over a shared wireless communication medium; and a channel access module configured for maintaining data blocks for transmission to multiple wireless receivers over the wireless communication medium, wherein the data blocks are organized based on access categories; wherein upon successful contention by each access category for a transmission opportunity period for access to the wireless communication medium, during the transmission opportunity period the channel access module utilizes the physical layer for transmitting one or more data blocks of a primary access category to one or more primary destination wireless receivers, while simultaneously transmitting one or more data blocks of one or more secondary access categories to one or more secondary wireless receivers, over the wireless communication medium.
 16. The wireless station of claim 15, wherein: the data blocks are organized into access categories in order of transmission priority; and the wireless station comprises a multiple-input-multiple-output (MIMO) wireless station.
 17. The wireless station of claim 16, wherein the transmission opportunity comprises a multi-user transmission opportunity (MU-TXOP) for simultaneous transmission of data blocks at different transmission priorities during the MU-TXOP over the wireless communication medium.
 18. The wireless station of claim 15, wherein: contending for the transmission opportunity period comprises each access category contending for access to the wireless communication medium based on a value of a respective backoff timer and transmission priority; and the channel access module is configured for directionally transmitting the data blocks of the primary access category to the one or more primary destination wireless receivers while simultaneously transmitting the data blocks of the one or more secondary access categories to the one or more secondary destination wireless receivers, over the wireless communication medium.
 19. The wireless station of claim 18, wherein: contenting for access to the wireless communication medium comprises performing Enhanced Distributed Channel Access (EDCA) to provide Quality of Service (QoS) for a data block in a high priority access category.
 20. The wireless station of claim 15, wherein: contending for a transmission opportunity period comprises performing Enhanced Distributed Channel Access (EDCA) to provide Quality of Service (QoS) for a data block in the primary access category; and the channel access module is configured for directionally transmitting the data blocks of the primary access category to the one or more primary destination wireless receivers, and simultaneously, transmitting the one or more data blocks of the secondary access categories to the one or more secondary destination wireless receivers, over the wireless communication medium.
 21. The wireless station of claim 20, wherein: each data block comprises a packet including an address of a destination wireless receiver; and the communication physical layer receives from each destination wireless receiver an acknowledgment after transmitting a packet intended for each destination wireless receiver.
 22. The wireless station of claim 21, wherein: the channel access module is configured for truncating the transmission opportunity upon transmission of a last data block of the primary access category.
 23. The wireless station of claim 22, wherein: the channel access module is configured for performing multi-user MIMO wireless transmission utilizing the physical layer via multiple antennas over the wireless communication medium.
 24. The wireless station of claim 23, wherein the wireless communication system comprises a wireless local area network.
 25. The wireless station of claim 20, wherein: a duration of the transmission opportunity period is based on a transmission opportunity period limit of the primary access category; at least one spatial stream set in each downlink multi-user MIMO PPDU physical layer convergence procedure (PLOP) protocol data unit (PPDU) packet includes only one or more MAC service data unit (MSDU) packets corresponding to the primary access category, wherein a stream set comprises a group of spatial streams of a downlink MU-MIMO PPDU packet intended for reception by a single destination wireless receiver over the wireless communication medium.
 26. The wireless station of claim 20, wherein: in contending for the transmission opportunity period, only EDCA parameters of the primary access category are used.
 27. The wireless station of claim 15, wherein: the channel access module is configured for resolving internal contention among the access categories by allowing the secondary access categories to share the transmission opportunity period.
 28. The wireless station of claim 27, wherein: when sharing the transmission opportunity period is not possible, the secondary access categories invoke communication medium access backoff.
 29. A wireless communication system, comprising: a wireless station; and a plurality of wireless receivers; the wireless station comprising: a communication physical layer configured for wireless communication over a shared wireless communication medium; and a channel access module configured for maintaining data blocks for transmission to the wireless receivers over the wireless communication medium, wherein the data blocks are organized based on access categories; wherein upon successful contention by each access category for a transmission opportunity period for access to the wireless communication medium, during the transmission opportunity period the channel access module utilizes the physical layer for transmitting one or more data blocks of a primary access category to one or more primary destination wireless receivers, while simultaneously transmitting one or more data blocks of one or more secondary access categories to one or more secondary wireless receivers, over the wireless communication medium.
 30. The wireless system of claim 29, wherein: the data blocks are organized into access categories in order of transmission priority; and the wireless station comprises a multiple-input-multiple-output (MIMO) wireless station.
 31. The wireless system of claim 30, wherein the transmission opportunity comprises a multi-user transmission opportunity (MU-TXOP) for simultaneous transmission of data blocks at different transmission priorities during the MU-TXOP over the wireless communication medium.
 32. The wireless system of claim 29, wherein: each access category contends for the transmission opportunity period by contending for access to the wireless communication medium based on a value of a respective backoff timer and transmission priority; and the channel access module is configured for directionally transmitting the data blocks of the primary access category to the one or more primary destination wireless receivers while simultaneously transmitting the data blocks of the one or more secondary access categories to the one or more secondary destination wireless receivers, over the wireless communication medium.
 33. The wireless system of claim 32, wherein: contending for access to the wireless communication medium comprises performing Enhanced Distributed Channel Access (EDCA) to provide Quality of Service (QoS) for a data block in a high priority access category.
 34. The wireless system of claim 29, wherein: contending for a transmission opportunity period comprises performing Enhanced Distributed Channel Access (EDCA) to provide Quality of Service (QoS) for a data block in the primary access category; and the channel access module is configured for directionally transmitting the data blocks of the primary access category to the one or more primary destination wireless receivers, and simultaneously, transmitting the one or more data blocks of the secondary access categories to the one or more secondary destination wireless receivers, over the wireless communication medium.
 35. The wireless system of claim 34, wherein: each data block comprises a packet including an address of a destination wireless receiver; each destination wireless receiver performs uplink (UL) transmission of an acknowledgment to the wireless station over the wireless medium, upon receiving a packet intended for that destination wireless receiver; and the channel access module is configured for truncating the transmission opportunity upon transmission of a last data block of the primary access category.
 36. The wireless system of claim 35, wherein: the channel access module is configured for performing multi-user MIMO wireless transmission utilizing the physical layer via multiple antennas over the wireless communication medium; and the wireless communication system comprises a wireless local area network.
 37. The wireless system of claim 34, wherein: a duration of the transmission opportunity period is based on a transmission opportunity period limit of the primary access category; at least one spatial stream set in each downlink multi-user MIMO PPDU physical layer convergence procedure (PLOP) protocol data unit (PPDU) packet includes only one or more MAC service data unit (MSDU) packets corresponding to the primary access category, wherein a stream set comprises a group of spatial streams of a downlink MU-MIMO PPDU packet intended for reception by a single destination wireless receiver over the wireless communication medium.
 38. The wireless system of claim 34, wherein: in contending for the transmission opportunity period, only EDCA parameters of the primary access category are used.
 39. The wireless system of claim 34, wherein: the channel access module is configured for resolving internal contention among the access categories by allowing the secondary access categories to share the transmission opportunity period, and when sharing the transmission opportunity period is not possible, the secondary access categories invoke communication medium access backoff.
 40. A method of wireless communication in a wireless communication system, comprising: receiving data blocks transmitted from a transmitting station over a wireless communication medium, wherein the data blocks are organized based on primary and secondary access categories; extracting, from the received data blocks, data blocks of the primary access category; and processing the data blocks of the primary access category.
 41. The method of claim 40, wherein: the data blocks are organized into the primary and secondary access categories in order of transmission priority; and the transmitting station comprises a multiple-input-multiple-output (MIMO) wireless station.
 42. The method of claim 40, wherein: each data block comprises a packet including an address of a receiving station, and the method further comprises transmitting an acknowledgement after receiving a corresponding packet of the receiving station.
 43. A method of wireless communication in a wireless communication system, comprising: receiving data blocks transmitted from a transmitting station over a wireless communication medium, wherein the data blocks are organized based on primary and secondary access categories; extracting, from the received data blocks, data blocks of the secondary access category; and processing the data blocks of the secondary access category.
 44. A method of wireless communication in a wireless communication system, comprising: receiving data blocks transmitted from a transmitting station over a wireless communication medium, wherein the data blocks are organized based on the primary and secondary access categories; extracting, from the received data blocks, data blocks of the primary access category and data blocks of the secondary access category; and processing the extracted data blocks of the primary access category and the secondary access category. 